922 THE VOYAGE OF H.M.S. CHALLENGER. 



thin convex bow. In this way arises a very simple, equilateral triangular skeleton, with three equal 

 large meshes. 



Dimensions. Length of the spines 014, sides of the triangle 016. 



Habitat. Tropical Atlantic, Station 348, depth 2450 fathoms. 



2. Triplecta triactis, n. sp. (PL 91, fig. 7). 



Spines straight, equal, three-sided prismatic, pinnate, each with three to four pairs of opposite 

 slender pinnulse or lateral branches ; the pinnules of each spine are correspondingly parallel to the 

 main rods of the other two spines. All pinnulse branched and connected by a few slender bows, 

 marking the sides of a regular triangle. 



Dimensions. Length of the spines 015, sides of the triangle 017. 



Habitat. Central Pacific, Station 272, depth 2600 fathoms. 



Genus 394. Plectophora, 1 Haeckel, 1881, Prodromus, p. 424. 



Definition. P lectanida with three radial spines, arising from one common 

 central point and corresponding to the edges of a three-sided pyramid. 



The genus Plectophora has been derived from Plagiacantha by union of the meeting 

 neighbouring branches of the three radial spines, and exhibits therefore to it the same 

 relation that Triplecta bears to Triplagia. The loose framework so produced corre- 

 sponds to the three sides of a flat pyramid and supports the central capsule. 



\ 



1. Plectophora triomma, n. sp. 



Spines equal, straight, three-sided prismatic, thorny, connected by three convex bows, the 

 meeting branches of lateral spines arising in one pair from the middle part of each spine. There- 

 fore the skeleton exhibits three large ovate meshes only. 



Dimensions. Length of the spines 012, of the meshes 0'08. 



Habitat. North Pacific, Station 238, surface. 



2. Plectophora arachnoides, Haeckel. 



Plagiacantha arachnoides, var., Claparfede, 1858, Etudes sur les Infusoires et les Ehizopodes, 

 p. 462, Taf. xxii. fig. 9. 



Spines straight, cylindrical, trifid, with one pair of lateral branches. The nine diverging, 

 straight, and smooth branches are connected in the distal part by slender concave bows, so that the 

 whole skeleton exhibits nine wide meshes, three larger pentagonal and six smaller triangular. 



Dimensions. Length of the spines 014, of their branches P 07. 



Habitat. North Atlantic, west coast of Norway (Claparede), surface. 

 1 Plectophora = Bearing a hunting net ; 



